1. Discussion of the Background Art
State of the art. Many designs of fixed, mobile or portable passive i.e. absorption—or “active” electrostatic or magnetic—i.e. deflecting—nuclear radiation shields are known in the literature, to protect the personnel and equipment from nuclear radiation coming from sources on the Earth, from the Sun, or from the cosmos. These shields are aimed to protect personnel and equipment from harmful nuclear radiation, including X radiation. In general, these shields are omni-directional, in the sense that they attenuate evenly radiation coming from any direction of space. The disadvantages of these shields are that they are massive and that they offer enough protection only when they have a large thickness and correspondingly high mass. Such shields are costly and, because of their high mass, are difficult to be used in space systems and, generally, in mobile systems. The known shields also have the disadvantage of the total lack of adaptability to the possible changes of the external radiation sources.
Especially for vehicles, for which the volume occupied by the equipments and the weight are essential factors, heavy and bulky shields are impractical. Moreover, for vehicles, the direction and the amplitude of the radiation sources are fluctuating and, in general, are unknown. Such vehicles are space vehicles, mobile radiological laboratories for medical or industrial use, and de-contamination vehicles. For such cases, an adaptive shield is needed.
Space vehicles represent a special case, as they require radiation shields adaptive to changes in the level of cosmic radiation. The adaptation could reasonably reduce temporarily the protected space in case of intense radiation, such that the protection is ensured for the personnel and for the most critical equipment, even if the comfort is decreased. Adaptive shields are also needed in the case of terrestrial vehicles, to ensure protection depending on the conditions on the terrain. Moreover, in the case of surface exploration vehicles, the shielding system will have to adapt to the Sun's movement relative to the planet's surface. Space stations can be considered a specific type of space vehicle, where long-duration stays make astronauts especially vulnerable to radiation. It is known that space stations, such as ISS, must be provided with “safe areas” where the personnel on the station can take refuge when dangerous solar or galactic radiative events occur. Vehicles for long space travels and stations on other planets or on satellites, as planned today for the near future, need safe areas that are well shielded to offer protection to the personnel under extreme space weather.
In general, in all situations where variable radiation sources are encountered, adaptive shields are required to achieve an optimal balance between the radiation protection and the volume of the protected space.
Even only for the psychical “safety” condition of people working in radiation conditions, such a shield would be desirable and useful.
It is known that space systems can be exposed, for short periods of time, to very intense fluxes of radiation, which come from well-defined directions from space, as the Sun or a particular galaxy. Such events happen during solar flares or during strong extra-solar nuclear activity—galactic or extragalactic, as supernovae explosions. Under these conditions, personnel or critical equipment onboard space systems are in major hazard. The hazard—probability of irradiation over a maximum acceptable dose—rises in case of extended space travel. Moreover, the inception and the development of space industrial activities and of space tourism impose reconsidering the problem of irradiation risks and of designing radiation shields that provide protection to passengers in conditions of large variability of space irradiation.
It is known that outside the space protected by Earth's magnetic field—outside the magnetosphere—radiation can accidentally become very intense. For example, it is known that between the missions Apollo 16 and 17, a strong proton radiation was produced, which, if astronauts were on route to the Moon, would have irradiated them with a lethal dose in less than 10 hours. It is also known that, during solar flares, X radiation—band 1.0-8.0 Angstrom—can reach the flux of 10−3 W/m2, while in the absence of solar flares, its value is around 10−7 W/m2—NASA, http://science.nasa.gov/headlines/y2000/ast14jul—2m.htm. Such increases, of up to four orders of magnitude, over short periods of time—minutes or hours—may endanger the lives of passengers of a space station, or space vehicle.
Due to the fact that radiation events are both rare and unpredictable, protection through massive omni-directional shielding is too costly. The cost of a radiation shield is a major factor in all instances in which radiation protection is required. In the case of shielding vehicles or portable equipment—for example, radiation protection clothing—mass is an essential factor. The problem exposed above is extensively dealt with in the recent volume “Space Radiation Hazards and the Vision for Space Exploration. Report of a Workshop” by the Ad Hoc Committee on the Solar Radiation Environment and NASA's Vision for Space Exploration; National Research Council of the National Academies, http://books.nap.edu/openbook.php?record_id=11760&page=R1, accessed Jan. 2, 2007). Similar problems are encountered on satellites that carry sensitive electronic equipment that must be protected in case of intense solar or cosmic radiation.
Thus, in space applications, it is important to use shields with reduced mass, which will ensure protection according to necessity, that is, it is important to use adaptive shields. The solution currently used onboard space systems is an omni-directional shielding that ensures radiation protection inside a small portion of the spacecraft, where personnel can retreat in case of a significant increase in irradiation. Similar problems arise in the field of terrestrial installations.
While power grid failures induced by space radiation are largely known to occur due to the high currents induced in the cables due to the change in the magnetic fields, some equipment such as transformers are known to be the most vulnerable. It is not yet well understood if the direct radiation plays a part in the failure of power transformers; but it is known that a direct radiation hit is able to change the properties of the oils in the transformer and thus it could prove that the direct radiation hit may also play a role in the power grid failures. Therefore, it may be of interest to shield such equipment to radiation. Because the radiation direction is not fixed, an adaptive shield may also be beneficial for protecting power equipments.
Various designs of radiation shields are known in the literature. These shields can be fixed, mobile, or even portable. Such shields are used in a variety of applications. Examples of shield designs are (Radiation protection shield for electronic devices. Inventor: Katz Joseph M. US2002074142-2002-06-20), (Radiation protection concrete and radiation protection shield. Inventor: Vanvor Dieter. TW464878-2001-11-21), (Radiological shield for protection against neutrons and gamma-radiation, Riedel J., GB1145042-1969-03-12), (Shield for protection of a sleeping person against harmful radiation. Inventor: Jacobs Robert. U.S. Pat. No. 4,801,807-1989-01-31), (Shaped lead shield for protection against X-radiation. Inventor: Hou Jun; Yunsheng Shi. Applicant: Hou Jun, CN2141925U-1993-09-08), (Filter for X Radiation, Inventor Petcu Stelian, 30.07.1996, Patent RO 111228 B1), (Radiation Passive Shield Analysis and Design for Space Applications, International Conference on Environmental Systems, Horia Mihail Teodorescu, Al Globus, SAE International, Rome, Italy, Jul. 11-15, 2005. SAE 2005 Transactions Journal of Aerospace, 2005-01-2835, March 2006, pp. 179-188). Other designs can be similar to designs of shields for other types of radiation; such designs are provided in (Shield device for the rear protection of an infrared radiation emitter apparatus, tubes and shields for implementing it. Inventor: Lumpp Christian, FR2554556-1985-05-10), (Shield for protection against electromagnetic radiation of electrostatic field. Inventor: Sokolov Dmitrij Yu.; Kornakov Nikolaj N., Applicant: Sokolov Dmitrij Yu.; Kornakov Nikolaj N., SU1823164-1993-06-23). All these designs are for fixed shields. Also, many materials and combinations of materials are known to be effective in radiation protection, for example (Patent RO 118913 B, Multi-layer screen against X and gamma radiation, Moiseev T., 30.12.2003), (Patent RO 120513 B1, X-ray absorbing material and its variants, Inventors: Tkachenko Vladimir Ivanovich, U A.; Nosov Igor Stepanovich, Ru; Ivanov Valery Anatolievich, U A; Pechenkin Valery Ivanovich, U A; Sokolov Stanislav Yurievitch, L V., 28.02.2006). Also, there are many manufacturers of radiation shielding plates and materials, for example (X-ray Protection Screen, Data Sheet, Apreco Limited, The Bruff Business Centre, Suckley, Worcestershire, WR6 5DR, UK., www.apreco.co.uk), (Premier Technology Inc., 170 E. Siphon Rd. Pocatello, Id. 83202, USA, Shielding Windows & Glass—Information & Tutorials, RD 50 X-Ray Protection Glass http://www.premiertechnology.cc/premier/RD50.cfm).
In a recent publication, “Space Radiation Hazards and the Vision for Space Exploration—Report of a Workshop”, Committee on the Solar System Radiation Environment, Space Studies Board, Division on Engineering and Physical Sciences, National Research Council of the National Academies, 2006, Washington D.C., www.nap.edu, in Section “Operational Strategies for Science Weather Support”, p. 47, FIG. 3.4, (http://books.nap.edu/openbook.php?record_id=11760&page=47), among other means for reduction of radiation, the following are proposed: passive shielding, [radiation] storm shelters, and reconfigurable shielding.” However, no example of reconfigurable shielding is provided. The solution we propose goes beyond simple reconfiguration, moreover proposes a specific way to improve the efficiency of the shielding, while preserving the weight of the shielding as low as possible.
The necessity of fast deploying radiation shields whose shape is modifiable according to necessities was recognized and shields have been proposed that are composed of several movable shielding plates that can be position according to the necessity (Baudro, 1987), (Toepel, 2003). However, the arrangement of the component panels of the shield remain empirical and no specific manner of arranging them in connection to radiation dose minimization was presented in the patents (Baudro, 1987), (Toepel, 2003).
On the other hand, the minimization of the harmful radiation dose is a well established goal in medical applications of the nuclear diagnosis and treatment. The achievement of that goal was pursued in various technical solutions for the case of medical applications, especially for variable collimators (Short, 2005). Variable shape, reconfigurable collimators were proposed to achieve the said purpose. Short (Short, 2005) presented a radiation shield with variable attenuation that is essentially able to partly or completely interact with the radiation moreover that can change its structural properties at a microscopic scale in order to change its radiation attenuation. Short teaches a shield that is able to produce only intermediate levels of attenuation, between the attenuation provided when the slabs are perpendicular to the radiation propagation direction and zero attenuation.
However, the problem of applying specified distributions of radiation doses to specified parts of the patient body while using a radiation source or sources with well known positions and the problem of minimizing the radiation dose to personnel or equipment when the distribution of the radiation sources and the fluxes produced by the said sources are unknown and variable require different methods for reconfigurable the shielding. A highly adaptive reconfigurable shield and an appropriate adaptation method are needed in case of shielding against unknown, time-variable radiation sources as encountered in space. The adaptation should be performed for minimizing the radiation dose in the space delimited by the shield, while the space delimited by the shield must be at least a specified space to accommodate the protected personnel or the equipment.
The solution we propose solves the requirements above presented while departing from the known reconfigurable shields or collimators previously known. The solution relies on a specific way to improve the efficiency of the shielding by changing the arrangement of the shield elements, yet preserving the weight of the shielding as low as possible, where the improvement is obtained solely by increasing the thickness of the shield as apparent to the incident radiation.
2. The Technical Problem the Invention Solves
The first technical problem solved is the design of an adaptive radiation shield able to ensure an increased protection to radiation, especially when the radiation intensity and the direction from which the radiation comes are changing. The second technical problem solved is the design of the said adaptive radiation shield with a lower mass than a fixed shield made of the same materials.
The adaptive radiation shield and its constructive variants, as subsequently presented, according to the invention, solves the above-mentioned problems and eliminates or reduces the disadvantages of the classic designs.